The present invention relates to a carburetor for an internal combustion engine, especially for the internal combustion engine of a portable, hand-guided working tool such as a motor chainsaw etc., wherein the carburetor comprises a carburetor housing with intake channel and with a fuel channel opening into the intake channel. The fuel channel is connected to a fuel-filled control chamber of the carburetor and has a control valve arranged therein. The control member of the control valve is adjustable by a control screw that is mounted within the housing. For limiting the adjusting range of the valve member, a cap is fixedly mounted on the control screw and has a stop, whereby a counter stop connected to the carburetor housing is positioned in the rotational path of the stop at the cap.
Such a carburetor is known from U.S. Pat. No. 3,618,906. The fuel channel opening into the intake channel has a control valve which is embodied as a needle valve and whose control screw is screwed into the carburetor housing. In order to limit the adjusting range of the needle valve, a securing cap is snapped onto the knurled head of the control screw after a pre-adjustment has been performed at the manufacture. The securing cap has an outer stop, and a counter stop at the carburetor housing projects into the rotational path of this stop. The adjusting range of the control screw is thus limited to less than one complete rotation.
For securing the rotational position of the control screw springs, friction rings etc. must be provided.
As a function of the ambient temperature as well as of the altitude, the supplied fuel amount must be adjusted by rotation of the control screw. This is performed by the user whereby, depending on the dexterity of the user, a more or less satisfactory adjustment can be achieved.
It is therefore an object of the present invention to embody a carburetor of the aforementioned kind such that even an inexperienced user can perform the required adjustment of the fuel/air mixture to the operating condition in a simple manner.